==== Required information ====
- iRedMail version (check /etc/iredmail-release): version 2.4.0
- Linux/BSD distribution name and version: Ubuntu
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): MySQL
- Web server (Apache or Nginx): Apache
- Manage mail accounts with iRedAdmin-Pro? YES
- Related log if you're reporting an issue:
====

Dear all,
We having a problem when we try to send an email from a cpanel server to an iredmail server
we get this message.

LOG: MAIN
  cwd=/usr/local/cpanel/whostmgr/docroot 4 args: /usr/sbin/exim -v -M 1d7zBr-0004RW-Ot
delivering 1d7zBr-0004RW-Ot
Connecting to mx.salonatcom.com [192.81.221.68]:25 ... failed: Connection refused
LOG: MAIN
  H=mx.salonatcom.com [192.81.221.68] Connection refused
LOG: MAIN
  == customer.services@salonatcom.com R=dkim_lookuphost T=dkim_remote_smtp defer (111): Connection refused

Please note that sending and receiving emails throw iredmail server works fine when we send an email to it throw any mail client like gmail and even directly throw cpanel mail client but when we try to send an email throw php software on the server (Like contact us form) it didn't received.

I register my IP address on "Whitelisted senders" and "Whitelisted recipients" but still the problem is the same.

Any idea why is this?

Thanks in advance.